Electronic cameras image scenes onto a two-dimensional sensor such as a charge-coupled-device (CCD), a complementary metal-on-silicon (CMOS) device or other type of light sensor. These devices include a large number of photo-detectors (typically two, three, four or more million) arranged across a small two dimensional surface that individually generate a signal proportional to the intensity of light or other optical radiation (including infrared and ultra-violet regions of the spectrum adjacent the visible light wavelengths) striking the element. These elements, forming pixels of an image, are typically scanned in a raster pattern to generate a serial stream of data of the intensity of radiation striking one sensor element after another as they are scanned. Color data are most commonly obtained by using photo-detectors that are sensitive to each of distinct color components (such as red, green and blue), alternately distributed across the sensor.
A popular form of such an electronic camera is a small hand-held digital camera that records data of a large number of picture frames either as still photograph “snapshots” or as sequences of frames forming a moving picture. A significant amount of image processing is typically performed on the data of each frame within the camera before storing on a removable non-volatile memory such as a magnetic tape cartridge or a flash memory card. The processed data are typically displayed on a liquid crystal display (LCD) device on the outside of the camera. The processed data are also typically compressed before storage in the non-volatile memory in order to reduce the amount of storage capacity that is taken by the data for each picture frame.
The data acquired by the image sensor is typically processed to compensate for imperfections of the camera and to generally improve the quality of the image obtainable from the data. The correction for any defective pixel photodetector elements of the sensor is one processing function. Another is white balance correction wherein the relative magnitudes of different pixels of the primary colors are set to represent white. This processing also includes de-mosaicing the individual pixel data to superimpose data from spatially separate monochromatic pixel detectors of the sensor to render superimposed multi-colored pixels in the image data. This de-mosaicing then makes it desirable to process the data to enhance and smooth edges of the image. Compensation of the image data for noise and variations of the camera optical system across the image and for variations among the sensor photodetectors is also typically performed within the camera. Other processing typically includes one or more of gamma correction, contrast stretching, chrominance filtering and the like. Several of these image processing functions and others are described in an outline of Robert Kremens, “Fundamentals of Camera Image Processing,” dated May 2001, made available on the Internet by the Rochester Institute of Technology (R.I.T.), Center for Imaging Science, Digital Imaging and Remote Sensing Group, and Pixelphysics, Inc. It is the processed data that are displayed on the camera's LCD screen so that the displayed image appears to the user of the camera as it will when the stored data are later displayed or printed.
The processed data are also typically stored in a full frame buffer memory included in the camera. Data is then read from this buffer memory for compression by a data compression algorithm. A single frame may be compressed more than once by use of different compression algorithm parameters until the compressed data file conforms to some predetermined criteria, such as a total size less than some set limit. So uncompressed data of the full frame is stored in the buffer memory a period necessary for this compression processing to take place. Such a buffer is typically implemented by a volatile memory on an integrated circuit chip separate from a processor chip in the camera and is chosen to have a very fast access time.
Recyclable, single-use hand-held digital cameras for taking still photographs are also available. Such a camera is purchased by an end-user for a price that is much lower than that of a conventional digital camera. It is used by the end-user in a manner similar to a conventional digital camera, until a number of pictures have been taken to fill its internal non-volatile memory. At this point, the end-user returns the recyclable camera to a service center for processing of the stored pictures. Subsequently, the pictures are returned to the end-user as hardcopy prints or on a standard storage medium such as diskette or compact disk (CD). The camera is then refurbished by the service center, or the camera's manufacturer, including erasure of its internal memory, and then returned to a retail point-of-sale such as a camera store, drug store and the like to be resold—hence the term “recyclable”. A recyclable digital camera has only internal electronic memory for storage of pictures. It has no removable storage memory, no means for a user to display a captured image, and no means for the end-user to retrieve the stored pictures by transferring them to a personal computer. The stored pictures can only be retrieved by the service center by means available to the service center. The recyclable digital camera is analogous to a single-use photographic film camera in its model of manufacture, usage, processing and recycling to point-of-sale. For this business model to be viable, the recyclable digital camera is designed to be inexpensive to manufacture, and at the same time, the quality of the pictures delivered to the end user by the service center are made to be high. Currently, recyclable digital cameras use a method of capturing and storing data of pictures that is identical, or very similar, to that used in conventional digital cameras described above.
Because picture data compression is utilized in the recyclable camera, the number of pictures that can be stored in the camera is sufficient to make it attractive to end-users without the expense of a large internal non-volatile memory. The compression is performed using a method such that the resulting compressed picture is in a standard format used by a large majority of digital cameras, the JPEG standard format. The service center produces hardcopy prints from these JPEG format image files, or computer readable media carrying pictures in JPEG format, or both, depending upon requests of the customers.